Our invention is related to teleconferencing arrangements and, more particularly, to loudspeaking type teleconference systems.
Loudspeaking telephones, as is well known in the art, e.g., U.S. Pat. No. 3,046,354, issued to W. F. Clemency July 24, 1964, employ automatic gain adjustment in the transmitting and receiving channels responsive to the presence or absence of speech energy in one of the channels to control the direction of transmission. Such a voice-switched control arrangement provides a customer with a hands-free telephone instrument so that the customer is not restricted by the conventional handset.
Loudspeaking arrangements can be useful in a teleconferencing system wherein a number of conferees at one location are placed in communication with a number of conferees at a remote location via a telephone connection. The quality of the transmission between the two separated groups of conferees is generally dependent on the position of each conferee with respect to the microphone and loudspeaking device at each location. With a single microphone and loudspeaking device in the conference location room, the transmission is subject to degradation because some of the conferees are generally at a greater than optimum distance from the microphone and loudspeaking device.
It has previously been known to use a plurality of microphones appropriately spaced at each conferee location such as a conference room to improve the quality of the conference system. The microphone outputs are summed and the summed output is applied to the communication links between locations. In such an arrangement, each conferee can be within an acceptable distance from one of the microphones, whereby speech pickup is of relatively good quality. With all microphones turned on at one time, however, several undesirable effects occur. The total noise pickup is much greater than for a single microphone. The artificial reverberation effects occasioned by the delayed signal pickup from the more remote microphones severely lower the quality of the conference transmission. Further, electroacoustic instability can easily result from the plurality of the always turned on microphones. It is therefore desirable to provide a switching arrangement which permits only those microphones closest to the talking conferees to be active so that reverberation and noise pickup are minimized and additional gain may be inserted.
Techniques are well known for selecting a single microphone of a plurality of conferee microphones and for transmitting the signal from only the selected microphone. Such an arrangement is commonly known as a "voting circuit." In the "voting circuit" arrangement, the loudest talker can capture control and lock out the other conferees at his location. Automatic switching between microphones responsive to the highest speech level at the microphones may also result in transmission interruptions which adversely affect intelligibility and can result in unwanted interference occasioned by transient room noise. For example, a loud noise at one of the conference locations may completely turn off the controlling microphone. Further, since only one microphone is operative at a time, transfer of control from one microphone to another such as occasioned by the talking conferee moving from one position to another in a room location can result in speech transmission of varying quality, interruptions in transmission, and reverberation effects which vary with the talking conferee's position. Further, for good acoustical stability, any microphone which is on should be able to influence and actuate the loudspeaker source closest to it without necessarily reducing the output levels of other loudspeaking devices at more remote positions at the location.
Manually switching microphones on and off as needed is workable but is generally not useful, since it requires that each conferee by constantly alert to actuate his microphone switch when he wished to talk.
In one type of prior art conference system disclosed, for example, in U.S. Pat. No. 3,395,255, issued to F. J. Clement, a plurality of microphones and loudspeaking devices are placed in each conference room or location. Each mircophone is connected to an individual voice-switched network and the outputs of the individual voice-switched networks are combined. The combined output is applied to a telephone line via a common voice-switched network, and a plurality of loudspeaking devices are commonly connected to the common voice-switched network. The individual voice switched networks are responsive to the combined output to maintain a constant output level. While one microphone generally captures control, a plurality of microphones can be active concurrently. The common voice-switched network, however, controls the direction of transmission in the telephone line. In a conference hookup between first and second locations, the conferees at the first location hear the talking conferee at the first location. A conferee at the second location, however, will not hear the talking conferee at the first location if the direction of transmission controlled by the common voice-switched networks is from the second location to the first location. In such an arrangement, the conference hookup allows only one-direction transmission at a time between locations.
The common voice-switching network, in providing transmission from only one location at a time, of course, prevents regenerative feedback or singing. But the requirement of such unidirectional transmission between the two locations gives rise to a considerable impediment in the conference hookup. It is an object of our invention to provide a loudspeaking teleconferencing system for a plurality of remote room locations in which speech pickup, transmission, and distribution are not adversely affected by the use of a plurality of microphones and loudspeaking devices at each of a plurality of conference room locations.